This invention relates generally to gas turbine engines, more particularly to methods and apparatus for controlling engine clearance closures.
Known turbine engines include a compressor for compressing air which is suitably mixed with a fuel and channeled to a combustor wherein the mixture is ignited for generating hot combustion gases. The gases are channeled to at least one turbine, which extracts energy from the combustion gases for powering the compressor, as well as for producing useful work, such as propelling a vehicle.
To support engine casings and components within harsh engine environments, at least some known casings and components are supported by a plurality of support rings that are coupled together to form a backbone frame. The backbone frame provides structural support for components that are positioned radially inwardly from the backbone and also provides a means for an engine casing to be coupled around the engine. In addition, because the backbone frame facilitates controlling engine clearance closures defined between the engine casing and components positioned radially inwardly from the backbone frame, such backbone frames are typically designed to be as stiff as possible.
At least some known backbone frames used with recouperated engines, include a plurality of beams that extend between forward and aft flanges. To provide structural support and stiffness for the backbone frames, the beams are sized with a width that is substantially constant along a length of the beam, such that the width is as wide as possible, while still permitting physical passage of components and/or services therebetween. The beams are also sized with a thickness that is substantially constant along the beam length, and is limited by thermal induced stresses and component low cycle fatigue (LCF) considerations. More specifically, thicker and wider beams result in a stiffer structure, but are also more susceptible to thermally induced stresses and LCF. Alternatively, thinner and less wide beams are not as susceptible to thermally induced stresses and LCF, but may not provide the necessary stiffness to control engine clearance.